Prior attempts to achieve acceptable flame-retarded polyester/cotton blends have not met with commercial success. None of the treatments is practical from the consumer point of view, producing fabrics that have a very stiff hand. This is because in order to achieve the requisite flame-retardant properties, a high chemical add-on is required. This add-on makes the fabric stiff, masks the color of the underlying fabric, and often imparts an acrid or unacceptable odor to the fabric. In addition, the performance of the flame-retardant treated fabrics is often unreliable.
Most of the previous work conducted on flame-retardant (hereinafter sometimes "FR") polyester/cotton blends used a single chemical system that was targeted for the cotton component of the blend. The approach was to "load" the fabrics with a flame-retardant specific for cotton, for instance THPS [tetrakis-(hydroxymethyl)phosphonium sulfate]. It was not unusual with these earlier products to use from 30 to 35% of fixed chemical add-on in order for the polyester/cotton blend fabric to pass a bottom vertical flame test. Regrettably, however, the aesthetics of the finished fabrics were poor, as they had a very stiff hand and the appearance of a coated fabric. The add-ons used for these products were far in excess of the theoretically required amounts.
When THPS is applied to a polyester/cotton blend, about 3% of fixed phosphorus is required to achieve flame-retardant results. Since the THPS is specific to cotton, it does not react with the polyester content of the fabric but simply physically coats the polyester. As a result, after multiple launderings, that portion of the flame-retardant surrounding the polyester fiber is partially lost. In consequence, it was not unusual to use as much as 5.5% phosphorus add-on for a polyester/cotton blend, at least initially, in order to result in the target 3% of fixed phosphorus after 50 launderings in hot water.
In the 1970's, polyester/cotton blends were flame retardant treated using tris-2,3-dibromopropyl phosphate ("tris") in combination with THPS. However, "Tris" was found to be a carcinogen and was withdrawn from the market, so that there is no predominantly-polyester blend of polyester and cotton sold today that has been treated with flame-retardant chemicals. An object of the present invention is to produce acceptable flame-retardant treated polyester/cotton blends using multiple flame-retardant chemicals or chemical systems, and to employ processing conditions or adjuvants that produce a commercially acceptable attractive product having good color and acceptable hand.